In this study cell surface changes associated with the in vitro growth and development of dissociated embryonic cerebrum cells, and the maturation of cultured oncogenic, transformed nervous system cells will be determined. More specifically studies will be continued to 1) try to improve upon the purity of the neurons grown in vitro after centrifugal elutriation of dissociated embryonic rat cerebra; and 2) to elucidate some of the cell surface changes in neuroblastoma cells as they change from the pre-confluent to the post-confluent stage of growth in vitro. In addition in vivo studies designed to determine why neonatal mice are less susceptible than adult mice to neuroblastoma development upon challenge with neuroblastoma cells will be continued.